The invention relates to a circuit arrangement for the demodulation of a phase modulated signal which is obtained by the modulation of one or a plurality of carriers, the frequencies of which are multiples of a fundamental frequency. The signal consists of consecutive modulation sections and is conducted to an analogue multiplier. An integrator is also provided which is supplied with the output signal of the multiplier and which emits a demodulated signal.
In a known circuit arrangement for the demodulation of a phase modulated signal this phase modulated signal is conducted to a multiplier and a multiplicative signal is obtained which corresponds to the multiplication of the phase modulated signal with the carrier. This multiplicative signal is conducted to an integrator, from the output of which the demodulated signal is emitted. In order to use for integration only those parts of the multiplicative signal which are not affected by any phase shifts in the phase modulated signal, either in the transmission path between the multiplier and the integrator or within the integrator, there is provided an analogue switch which allows response to only those parts of the multiplicative signal which are unaffected by phase shifts in the phase modulated signal. Thus, undesired parts of the multiplicative signal are suppressed using this type of analogue switch. For example, an analogue switch of this type can be composed of a plurality of transistor stages.
The known circuit arrangement for the demodulation of a phase modulated signal possesses the disadvantage of a lack of temperature stability because the analogue switch, which consists of a plurality of transistor stages, displays differing swtiching behavior at different temperatures. This type of analogue switch itself necessitates a relatively large financial outlay for the circuitry, which increases in accordance with the requisite temperature stability of the analogue switch. In spite of this high outlay it is not possible to prevent signal distortions which arise as a result of the use of the described analogue switch.
An object of the invention is to provide a circuit arrangement for the demodulation of a phase modulated signal which is distinguished by a good temperature stability and a low circuitry cost.